Pulse jet burner



Sept. 30, 1969 F. HAAG PULSE JET BURNER Filed Dec. 20, 1967 UnitedStates Patent 3,469,929 PULSE JET BURNER Franz Haag, Plochingen,Germany, assignor to Junkers & Co. GmbH, Wernau (Neckar), Germany FiledDec. 20, 1967, Ser. No. 692,093 Int. Cl. F23c 3/02 US. Cl. 431-1 11Claims ABSTRACT OF THE DISCLOSURE A pulse jet burner having a combustionchamber, a resonance duct communicating with one end of the combustionchamber, and mixing tube means for feeding a mixture of combustion airand fuel into the combustion chamber and constructed in such a manner soas to impart at least to the combustion air passing therethrough arotary movement to enhance intimate mixing of air and fuel shortlybefore the same enter the combustion chamber.

BACKGROUND OF THE INVENTION The present invention relates to a pulse jetburner having at least one combustion chamber and a resonance ductcommunicating with one end of the latter, in which a mixing tube forfeeding a mixture of combustion air and fuel feeds this mixturelaterally into the combustion chamber.

In order to provide a high output pulse jet burner with a relativelysmall combustion chamber, which will permit use of the pulse jet burneras a household implement, for instance as a heat source for a centralheating plant of a home, it is necessary that the pulsating combustionswill follow each other at short intervals. This means that there will beonly a very short time available for filling the combustion chamberbetween the successive combustion periods with the necessary air-fuelmixture. Advantageously, feeding of air and fuel into the combustionchamber is not controlled by valves, and in this case it is necessarythat air and fuel are mixed with each other only in close proximity tothe combustion chamber, since otherwise, especially with easilyignitable fuels, the igniting and combustion zone moves into the conduitwhich feeds the mixture into the combustion chamber so that thecombustion of the mixture will start in the aforementioned conduit. Whenthis happens, the operating frequency of the pulse jet burner, to whichthe size and lengths of the combustion chamber and the followingresonance tube are tuned, will be changed so that the pulsatingcombustion will get out of step, or at least the output of the burnerwill be reduced by the change in frequency and by uncomplete combustionof the mixture. These disadvantages occur especially in pulse jetburners in which a gas is used as fuel, since the various fuel gaseswhich are used in industrial and domestic plants are differentlyignitable so that combustion in the mentioned pulse jet burner wouldstart at different localized zones resulting also in different operatingfrequencies.

It is an object of the present invention to eliminate the abovedisadvantages in pulse jet burners of the aforemen tioned kind.

It is a further object of the present invention to provide a pulse jetburner of the aforementioned kind in which an intimate mixture ofcombustion air and fuel is obtained over a short path to assure therebya uniform combustion independent of the relative ignitability of theused fuel.

It is an additional object of the present invention to provide for apulse jet burner of the aforementioned kind which is composed ofrelatively few and simple parts, so

3,469,929 Patented Sept. 30, 1969 that the burner may be manufactured atreasonable cost and stand up properly after extended use.

SUMMARY OF THE INVENTION With these objects in view, the pulse jetburner according to the present invention mainly comprises at least onecombustion chamber, mixing tube means for feeding a mixture ofcombustion air and fuel into the latter, the mixing tube meanscomprising outer tube means communicating at one end with the combustionchamber, a sleeve having a diameter smaller than the outer tube meansand being coaxially arranged in the latter so as to define with theinner surface of the outer tube means and the outer surface of thesleeve an annular gap, the sleeve having one end axially spaced from theone end of the outer tube means, means for closing the annular gap atthe other end of the sleeve, a first conduit communicating with theother end of the sleeve for feeding combustion air into the latter, asecond conduit communicating with the annular gap for feeding fuel intothe latter, and means in the sleeve for imparting to the combustion airpassing therethrough a twisting movement to provide an increased mixingaction combustion air and fuel in the space between the one end of thesleeve and the one end of the outer tube means; and a resonance ductcommunicating with the interior of the combustion chambers spaced fromthe one end of the outer tube means. The means for imparting a twistingmovement to the combustion air are preferably constituted by a spirallywound sheet metal member in the sleeve.

Very stable operating conditions of the pulse jet burner according tothe present invention are obtained, on the one band, due to the mixingof combustion air and fuel only a short distance before the mixtureenters into the combustion chamber, and, on the other hand, due to theintimate mixing of fuel and air obtained by the spirally wound sheetmetal member in the sleeve which imparts to the incoming air a rotarymovement so that the centrifugal forces imparted to the air will forcethe latter, as it leaves the sleeve, against the inner surface of theouter tube so as to be thoroughly mixed with the fuel which passesthrough the annular gap between the inner surface of the outer tube andthe outer surface of the sleeve.

In a preferred form the spirally wound sheet metal member extendsthrough the length of the sleeve and is twisted through an angle of, atleast degrees.

It is also possible to provide means in the annular gap so that the fuelwill be fed only through an angular portion of the annular gap. Theannular gap may be divided for this purpose by two diametricallyoppositely arranged webs into two separated, longitudinally extendingcompartments, only in one of which fuel is fed, and the twolongitudinally extending webs may be bent at the one end of the sleevein the same sense as the spirally wound sheet metal in the sleeve. Anincreased movement of the combustion air in radially outward directionmay also be obtained by providing at the other end of the sleeve acalotte concentrically arranged therewith, and with the concave side ofthe calotte facing towards the interior of the sleeve. This calotte thuscovers a central portion of the cross section of the sleeve so that theair is guided in an annular stream onto the spirally wound sheet metalmember in the interior of the sleeve. It is also advantageous to formthe cross section of the annular gap at the one end of the sleevesmaller than the remainder of the annular gap.

By dividing the annular gap by the webs into two longitudinallyextending compartments and by bending the end portions of the annularwebs and feeding fuel,

especially a fuel gas, only in one of the compartments, a rotarymovement is imparted also to the fuel gas. This rotary movement willoccur in the same sense as the rotary movement of the combustion airpassing through the sleeve whereby any essential braking of the twostreams during the mixture thereof is prevented, which would occur ifthe fuel stream would make a rotary movement opposite to that of the airstream. Nevertheless, an intimate mixture of the two streams isobtained, since the air and the fuel pass at different speeds to theregion where they are mixed with each other. Due to the speed differencean optimum mixing of the two components is quickly obtained, which iseven enhanced when gas is used as fuel since the lighter fuel gas willmove in a spiral radially inwardly, whereas the heavier air will bedriven radially outwardly due to the rotation thereof.

With a, pulse jet burner according to the present invention it ispossible to burn fuels with different ignition points completely andwithout causing any deviation from the proper operation of the burner.If fuel with a relatively low ignition point is used, the combustionprocess will be supported due to a relative circulation from thecombustion chamber in direction toward the region where the mixturetakes place, which will necessarily occur due to the rotary movement ofthe mixed components, so that a hot component mixture will pass from thecombustion chamber into the mixing tube causing thereby combustion ofthe fuel. The feeding speed of air and fuel into the mixing tube mayhowever be chosen in such a manner so that only a relative and not anabsolute back flow from the combustion chamber into the mixing tube willoccur so that in the region of the intermixing of the two components noundesired dilution of the forming mixture with burned gas will takeplace. An undesired dilution of the incoming mixture by burned gas isalso prevented according to the present invention by the calotte whichis arranged at the inlet end of the sleeve and facing with its concaveside the interior of the latter, which calotte will thus provide indirection of the back flow a flow resistance which is three timesgreater than in the direction of inflow of the air. In addition, it ispossible to provide the conduit which feeds air into the sleeve with agreater diameter than that of the sleeve which likewise results in anincrease of the flow resistance of any back flow. A similar action isobtained by making the cross section of the annular gap between thesleeve and the outer tube of the mixing tube means at the downstream endof the sleeve smaller than the remainder of the annular gap.

An especially advantageous construction may be obtained when the outertube means comprises in the region of the sleeve an intermediate tubeportion releasably connected to the first conduit.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic overall view of apulse jet burner according to the present invention;

FIG. 2 is an axial cross section through the mixing tube means and anadjacent portion of the combustion chamber; and

FIG. 3 is a cross section taken along the line III-III of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 schematically illustratesa pulse jet burner according to the present invention used as a heatingsource for a continuous water heater for production of hot water and/orfor heating water for a central heating plant. The pulse jet burnershown in FIG. 1, comprises two combustion chambers 10 and 11, resonanceducts 12 and 13 respectively communicating at one end thereof with oneend of the respective combustion chamber and at the other end thereofwith a common discharge opening 14, and mixing tube means for feeding amixture of combustion air and fuel into the combustion chambersintermediate the ends thereof. Sound absorbing chambers usually providedin pulse jet burners of this type are not illustrated in the drawing forsimplification reason. The water to be heated by the burner according tothe present invention is in a known manner guided through a conduit 15which extends from its inlet end 151 connected to a cold water supply,not shown, in spiral form first about the exterior of the combustionchamber 10 in upward direction, then in another spiral about theexterior of the second combustion chamber 11 in a downward direction topass finally through closely arranged heat exchange discs 17, providedat downstream end portions of the combustion chambers, to the outlet end152 of the tube 15 which is connected, in a manner not shown in thedrawing, to a pipe which leads the heated water to a point of use.

Combustion air is fed to the two combustion chambers 10 and 11 from aspace 20 through two air conduits 18 and 19, whereas fuel is fed througha fuel conduit 21 into a chamber 22 from which two conduits 23 and 24lead respectively to mixing tube means 25 and 26 where the fuel isintermixed with the air coming through the conduits 18 and 19.

FIG. 2 illustrates the mixing tube means 26 for the combustion chamber11 at an enlarged scale. The mixing tube means 26 illustrated in FIG. 2comprises a connecting socket 111 communicating at one end thereof withthe combustion chamber 11 and connected at the other end thereof to oneend of an intermediate tube portion 27, to the other end of which theair conduit 19 is connected by means of a screw cap 28, screwed onto thethreaded other end of the intermediate tube portion 27. The screw cap 28secures also an annular member 29 in the region of the other end of theintermediate tube portion 27 by clamping a radially outwardly extendingflange of the annular member 29 between the other end of theintermediate tube portion 27 and a corresponding flange on the end ofthe air conduit 19. The annular member 29 carries, integrally formedtherewith a sleeve 30 projecting toward the combustion chamber 11 andhaving an outer diameter smaller than the inner diameter of theintermediate tube portion 27 so as to form with the latter an annulargap 31 between the outer surface of the sleeve 30 and the inner surfaceof the intermediate tube portion 27. The annular gap 31 is divided bytwo diametrically oppositely arranged and longitudinally extending webs32 into two halves or two compartments and the fuel conduit 24communicates in substantially tangential direction only with one ofthese compartments, as best shown in FIG. 3. The two longitudinallyextending webs 32 are in the region of the discharge opening 33 of theannular gap 31 bent as indicated at 321, whereby a rotary movement isimparted to the fuel passing through the discharge end 33 of the annulargap. The annular gap 31 is at the end thereof distant from thecombustion chamber 11 closed by the annular member 29 which carries thesleeve 30 and the annular member 29 forms, therefore, means for closingthis end of the annular gap. As clearly shown in FIG. 2, the crosssection of the discharge end 33 of the annular gap is smaller than thecross section of the remainder of the annular gap and reduction of thecross section of the annular gap at the discharge opening 33 is obtainedby the frustoconical configuration 34 of the inner surface of theintermediate tube portion 27 in the region of the left end, as viewed inFIG. 2, of the sleeve 30. The inclination of the frustoconical surfaceportion 34 is at least 30 degrees.

Means are provided in the interior of the sleeve to impart to thecombustion air passing there through a rotary movement, and these meansare preferably formed by a spirally wound sheet metal member 35 whichextends longitudinally through the whole length of the sleeve 30 andthrough the annular member 29 and which, in the illustrated embodiment,is spirally twisted through an angle of about 120 degrees. A calotte 36is fastened concentrically with the annular member 29 to the right end,as viewed in FIG. 2, of the spirally wound sheet metal member 35, withthe concave side of the calotte 36 facing the interior of the sleeve.The calotte 36 has a diameter smaller than that of the inner diameter ofthe annular member 29 and covers the central portion of the latter. Theinner diameter of the annular member 29 gradually decreases from theright or inlet end thereof over part of the length of the annular memberfrom a miximum diameter substantially equal to the inner diameter of theconduit 19 to a minimum diameter substantially equal to the innerdiameter of the sleeve 30 so that the flow resistance of the incomingair is reduced. A rotary movement is imparted to the air passing fromthe conduit 19 into the interior of the sleeve 30, which sleeve isexchangeable arranged in the intermediate tube portion 27, by thespirally Wound sheet metal member 35 located in the sleeve, so that theair leaving the discharge end of the sleeve is guided in radiallyoutward direction onto the inner surface of the left end portion, asviewed in FIG. 2, of the intermediate tube portion 27 and onto the innersurface of the connecting socket 111 bordering thereon. This guiding ofthe air in a rotary annular stream is initiated by the central calotte36. A rotary movement in the same sense, as imparted to the air stream,is also imparted to the fuel, which passes through one-half of theannular gap 31 and through the discharge opening 33 of this gap, by thebent end portions of the longitudinal webs 32 so that the fuel is guidedin a stream having the shape of the half hollow cylinder into the fastrotating peripheral air stream to be thereby intimately mixed with thelatter. A back flow of the mixture from the combustion chamber 11 intothe intermediate tube portion 27, created by the combustion of themixture in the combustion chamber, is braked to a considerable extent bythe concave surface of the callote 36, the considerable increase of theflow cross section at the junction of the conduit 19 and the right end,as viewed in FIG. 2, of the annular member 29, as well as by theincrease of the diameter of the inner surface of the intermediate tubeportion 27 at the frustoconical portion 34 thereof, so that anundesirable considerable dilution of the fuelair mixture in theintermediate tube portion 27 with combustion gases from the combustionchamber 11 can not take place.

The construction according to the present invention will provide astable operation of the pulse jet burner and will assure that fuel gaseswith different heat contents, ditferent ignition speeds and differentreaction times are burned substantially in the same perfect manner.

It will be understood that each of the elements described above, or twoor more together, many also find a useful application in other types ofpulse jet burners diifering from the types described above.

While the invention has been illustrated and described as embodied in apulse jet burner having mixing tube means in which a rotary movement isimparted at least to the air stream passing therethrough so as toprovide an intimate mixing of the air and fuel streams passing throughthe mixing tube means, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and. range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. In a valveless pulse jet burner, in combination, at least onecombustion chamber; mixing tube means for feeding a mixture ofcombustion air and fuel into said combustion chamber, said mixing tubemeans comprising outer tube means communicating at one end thereof withthe combustion chamber a sleeve having a diameter smaller than the outertube means and being coaxially arranged in the latter so as to definebetween the inner surface of the outer tube means and the outer surfaceof the sleeve and annular gap, said sleeve having one end axially spacedfrom said one end of the outer tube means, means closing said annulargap at the other end of that sleeve, a first conduit communicating withsaid other end of that sleeve for feeding combustion air into thelatter, a second conduit communicating with the annular gap for feedingfuel into the latter, and. means located in its entirety in said sleevefor imparting to the combustion air passing therethrough a twistingmovement to provide an increased mixing action between combustion airand fuel in the space between said one end of the sleeve and said oneend of the outer tube means; and a resonance duct communicating with theinterior of said combustion chamber spaced from said one end of saidouter tube means.

2. In a pulse jet burner as defined in claim 1, wherein said means forimparting a twisting movement to the combustion air comprises a spirallywound sheet metal memher in said sleeve.

3. In a pulse jet burner as defined in claim 2, wherein said spirallysheet metal member extends through the whole length of said sleeve andis twisted at least through an angle of degrees.

4. In a pulse jet burner as defined in claim 1, and including meansdividing said annular gap into two longitudinal extending compartments,said second conduit communicating only with one of said compartments.

5. In a pulse jet burner as defined in claim 2, and including a pair ofdiametrically opposite webs extending longitudinally through saidannular gap between the inner surface of said outer tube means and theouter surface of said sleeve and dividing the annular gap into twolongitudinally extending compartments, said second conduit communicatingonly with one of said compartments.

6. In a pulse jet burner as defined in claim 5, wherein end portions ofsaid webs in the region of said one end of said sleeve are bent in thesame sense as the spirally wound sheet metal member in said sleeve.

7. In a pulse jet burner as defined in claim 1, and including a calottehaving a diameter smaller than said sleeve and being arranged coaxiallywtih the latter in the region of said other end thereof, with theconcave side of said calotte facing the interior of said sleeve.

8. In a pulse jet burner as defined in claim 1, wherein the crosssection of said annular gap at said one end of said sleeve is smallerthan the cross section of the remainder of said gap.

9. In a pulse jet burner as defined in. claim 1, wherein said means forclosing said annular gap are integrally connected to said sleeve andtogether with the latter exchangeably mounted in said outer tube means.

10. In a pulse jet burner as defined in claim 1, wherein said outer tubemeans comprises in the region of said sleeve an intermediate tubeportion releasably connected to said first conduit.

. 7 8 11. In a pulse jet burner as defined in claim 1, whereinReferences Cited said resonance duct communicates with one end of saidUNITED STATES PATENTS combustion chambers substantially coaxiallytherewith 2,719,580 10/1955 Haag et a1. 431 1 and said mixing tube meanscommunicates with said com- 3,227,202 1/1966 Morgan 431*353 bustionchamber in the region adjacent to the other end 5 3 252 496 5 1966 H 311 thereof and extends transverse to the axis of said combustion chamber,EDWARD G. FAVORS, Primary Examiner

